Five years ago at the inception of this grant, we presented the hypothesis that the expression of defects in the integrated control of cellular differentiation and proliferation served a significant role in carcinogensis. To test this hypothesis we first initiated studies to establish how the integrated control of differentiation and proliferation is regulated in normal cells and what events mediate these processes. We next performed experiments to determine if and how the induction of carcinogenesis with chemical and/or physical agents abrogates the integrated control of cellular differentiation and proliferation. Excellent progress has been made in all these studies| We established that the integrated control of differentiation and proliferation is mediated at a distinct cell cycle arrest state, that a specific sequence of biological events must occur as part of this regulatory mechanism, and that this regulatory process is evident both in murine mesenchymal stem cells and in normal human epidermal cells. In addition, we have made significant progress in identifying and purifying physiological regulatory molecules from human blood that control these processes. We also established that physical and chemical agents that initiate carcinogenesis or cause complete carcinogenesis can induce stable defects in the integrated control of cellular differentiation and proliferation in mesenchymal stem cells and preliminary results suggest that comparable events occur in normal human epidermal cells. We therefore now propose to expand these studies with the specific goal to establish the mechanisms that regulate the integrated control of cellular differentiation and proliferation and the mechanisms by which carcinogenic agents disrupt these critical regulatory processes.